In this patent application, the terms bridge, upper bridge and lower bridge are used to refer to the cross beams which are secured above and/or underneath the fabric over the weaving width of the machine and which serve to guide the fabrics in the direction of the place where the fabrics are rolled up onto rolls or folded in carts, away from the weaving reed.
In face-to-face weaving machines, two fabrics are woven simultaneously, usually one above the other, each of which comprises a base fabric consisting of weft yarns and warp yarns. In the case of weaving fabrics with cut pile, these base fabrics are connected to one another with the aid of pile warp yarns which move from the bottom base fabric to the top base fabric and vice versa in a pattern-forming manner.
During the weaving process, the two fabrics (which together form the non-separated face-to-face fabric) are then moved together through the opening formed between the upper bridge and the lower bridge. In this patent application, the space between the upper bridge and the lower bridge is referred to as the jaw. These two fabrics in the non-separated face-to-face fabric are kept apart over a distance which substantially corresponds to the distance between upper bridge and lower bridge (the jaw height). In some cases, use is additionally made of a lancet device comprising elongate metal strips (the lancets). A plurality of lancets extends in the warp direction over the width of the weaving machine into the jaw, between the lower and upper base fabric. The non-separated face-to-face fabric is then supplied to the cutting device which will use a cutting knife to perform a cutting operation, thus forming two fabrics with cut pile.
In single-face weaving machines, one single fabric consisting of weft yarns, warp yarns and pile warp yarns is woven. This fabric is guided along an upper bridge and/or a lower bridge. The position of the upper bridge (and thus the jaw height) can be readjusted on changing the fabric thickness.
The adjustment of this jaw is a delicate process involving:                setting a specific, exact value of the jaw height;        keeping the jaw height equal on the left and the right of the weaving machine;        in the case of a face-to-face weaving machine having a cutting device, keeping the cutting device in the correct position with respect to the jaw;        preventing or at least limiting the bending of the upper bridge and the lower bridge in order to minimize an uneven pile height over the width of the weaving machine.        
Belgian patent BE 1000995 describes a device which simplifies the adjustment of the jaw and which makes it no longer necessary to apply the ‘trial and error’ method in which the result of each adjustment of the jaw has to be assessed by weaving a piece of fabric. To this end, the cutting device is firstly provided with one or more electronic position sensors emitting a signal which is respectively in relation to the position of the upper bridge and the lower bridge with respect to the cutting knife. Secondly, the upper bridge and the lower bridge are each provided with adjusting spindles at their ends, which can optionally be driven by an electric motor in order to facilitate the adjustment of the upper bridge and the lower bridge. By readjusting the different adjusting spindles, it is possible to read and check the distances, on the one hand, between the upper bridge and the lower bridge and, on the other hand, between one of the bridges and a reference point on the weaving machine (upper or lower side of the cutting knife) or to use the processor unit to actuate the drive in order to thus reach the desired position.
However, the device described in BE 1000995 does not offer a simple and rapid solution for releasing the bridges before they are positioned and for re-securing these bridges once the desired position has been reached. Releasing and securing the bridges is a time-consuming process and is also ergonomically burdensome. The standard solution for securing a bridge is to fix it in various locations against the chassis of the weaving machine using bolts.